How to Keep Bagged Salad Fresh for as Long as Possible, According to Food Scientists

Whether you call them salad leaves or leafy greens, vegetables such as kale, spinach, and lettuces are some of the most versatile foods you can eat. They're right at home in myriad dishes, from colorful salads to hearty sandwiches. Leafy green vegetables are also teeming with essential nutrients, including vitamin C and calcium.

If you typically buy bagged greens, you've probably had the unfortunate experience of finding wilted, slimy leaves in the bag just a few days after purchasing. To find out how to keep bagged leaves fresh long enough to reach your plate, we asked food professionals to share a leaf out of their book.

The Right Way to Store Bagged Salad Leaves

Regardless of the type of leafy green vegetable, the same general storage rules apply. The optimal approach begins before you even get home from the supermarket by storing the greens in an insulated cooler bag, says Randy W. Worobo, professor of food microbiology at Cornell University. Otherwise, the package of greens will be exposed to ambient temperature before it enters the fridge, thereby increasing the risk of condensation (moisture). This can shorten the shelf life of your salad leaves, as moisture encourages rapid deterioration.

At home, place unopened bags of leafy greens straight into the refrigerator, says Worobo. Also, make sure your fridge is set to the correct temperature of 40 degrees Fahrenheit or below, as noted by the United States Department of Agriculture (USDA). This is essential for keeping food (leafy greens or otherwise) safe. If you're unsure of your fridge's temperature, put a refrigerator thermometer in the warmest part of your door—typically, close to the door—to monitor its temperature, says Ghaida Batarseh Havern, MS, food safety extension educator at Michigan State University.

After opening the bag of salad leaves, you'll want to continue minimizing condensation in the container, says Worobo. To do this, place a clean paper towel inside the bag and seal it with a chip clip. The paper towel will help absorb any condensation that might develop during storage.

What About Boxed Salad Leaves?

Use the same methods outlined above. In either case, the best place to store leafy greens in the refrigerator is in the crisper drawer, says Havern. This part of your fridge "will maintain high humidity and help the leafy greens stay fresh," she says.

You Don't Always Need to Toss Greens by the "Best By" Date

Most bags or boxes of salad leaves have a "best by" date. However, it's important to note that this date is different from an expiration date. According to Havern, the "best by" date is an indicator for quality, not food safety or science. In contrast, expiration dates refer to food safety, as they tell you the last day it's safe to eat the food. Therefore, if the "best by" date has passed, you might still be able to eat the greens—but they might not have the same quality, taste, and freshness as before, says Havern. "If the leaves still look firm and [there's] no visible deterioration of the leaf tissue, you can still use them," Worobo says.

Signs Leafy Greens Have Gone Bad

When it comes to salad leaves, common signs of spoilage include wilting, sliminess, foul odor, or change of color, says Havern. "You should also check the bottom of the bag, because spoilage may occur at the bottom of the bag first," says Worobo. Most notably, spoiled leaves will produce an off-colored liquid, which often accumulates at the bottom.

Buy Whole Head Lettuces and Greens for Longer Shelf Life

If you want salad leaves or leafy greens to last longer, consider choosing whole heads or bunches, rather than bagged greens. According to Havern, cutting or chopping produce changes the leaf's biochemistry, making the tissues vulnerable to bacterial contamination. Specifically, the cells in the tissues release their contents, which serve as food for spoilage microorganisms, says Worobo. And since the leaves in bags and boxes are often pre-cut, they generally have a shorter shelf life (three to five days) than whole heads (one to two weeks) after the date of purchase. Thus, buying whole heads of lettuce or bunches of spinach will let you determine when the leaves are cut. Not to mention, whole uncut vegetables are usually cheaper, so the switch will also help you save money on groceries.